Cómo navegar por las relaciones mediante propiedades de navegación (Entity Framework)

En este tema se muestra cómo navegar por las relaciones mediante propiedades de navegación. Para obtener más información, vea Propiedades de navegación. El ejemplo obtiene todos los pedidos de los contactos cuyo apellido sea "Zhou". La propiedad de navegación Contact.SalesOrderHeader se utiliza para obtener la colección de objetos SalesOrderHeader para cada contacto. El mismo ejemplo se muestra con cada una de las siguientes tecnologías de consulta de Entity Framework :

• LINQ to Entities

• Entity SQL con ObjectQuery<T>

• Métodos del generador de consultas de ObjectQuery<T>

El ejemplo de este tema se basa en el modelo AdventureWorks Sales. Para ejecutar el código de este tema, debe haber agregado el modelo AdventureWorks Sales al proyecto y haber configurado el proyecto para que use Entity Framework. Para obtener más información, vea Cómo: Usar el Asistente para Entity Data Model (Entity Framework) o Cómo: Configurar manualmente un proyecto de Entity Framework y Cómo: Definir manualmente un modelo Entity Data Model (Entity Framework).

Ejemplo

Este es el ejemplo de LINQ to Entities .

Dim lastName = "Zhou"
Using context As New AdventureWorksEntities
    Dim contacts As ObjectSet(Of Contact) = context.Contacts

    Dim ordersQuery = From contact In contacts _
        Where contact.LastName = lastName _
        Select New With _
                {.LastName = contact.LastName, _
                 .Orders = contact.SalesOrderHeaders}

    For Each order In ordersQuery
        Console.WriteLine("Name: {0}", order.LastName)
        For Each orderInfo In order.Orders

            Console.WriteLine("Order ID: {0}, Order date: {1}, Total Due: {2}", _
                    orderInfo.SalesOrderID, orderInfo.OrderDate, orderInfo.TotalDue)
        Next

        Console.WriteLine("")
    Next
End Using

string lastName = "Zhou";
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    ObjectSet<Contact> contacts = context.Contacts;

    var ordersQuery = from contact in contacts
                      where contact.LastName == lastName
                      select new { LastName = contact.LastName, Orders = contact.SalesOrderHeaders };

    foreach (var order in ordersQuery)
    {
        Console.WriteLine("Name: {0}", order.LastName);
        foreach (SalesOrderHeader orderInfo in order.Orders)
        {
            Console.WriteLine("Order ID: {0}, Order date: {1}, Total Due: {2}",
                orderInfo.SalesOrderID, orderInfo.OrderDate, orderInfo.TotalDue);
        }
        Console.WriteLine("");
    }
}

Este es el ejemplo de Entity SQL .

Using context As New AdventureWorksEntities()
    Dim esqlQuery As String = "SELECT c.FirstName, c.SalesOrderHeaders " & _
        " FROM AdventureWorksEntities.Contacts AS c where c.LastName = @ln"

    Dim query As New ObjectQuery(Of DbDataRecord)(esqlQuery, context)

    ' Add parameters to the collection. 
    query.Parameters.Add(New ObjectParameter("ln", "Zhou"))

    For Each rec As DbDataRecord In query

        ' Display contact's first name. 
        Console.WriteLine("First Name {0}: ", rec(0))
        Dim list As List(Of SalesOrderHeader) = TryCast(rec(1), List(Of SalesOrderHeader))
        ' Display SalesOrderHeader information 
        ' associated with the contact. 
        For Each soh As SalesOrderHeader In list
            Console.WriteLine(" Order ID: {0}, Order date: {1}, Total Due: {2}",
                              soh.SalesOrderID, soh.OrderDate, soh.TotalDue)
        Next
    Next
End Using

using (AdventureWorksEntities context =
    new AdventureWorksEntities())
{
    string esqlQuery = @"SELECT c.FirstName, c.SalesOrderHeaders 
        FROM AdventureWorksEntities.Contacts AS c where c.LastName = @ln";
    ObjectQuery<DbDataRecord> query = new ObjectQuery<DbDataRecord>(esqlQuery, context);
    query.Parameters.Add(new ObjectParameter("ln", "Zhou"));

    foreach (DbDataRecord rec in query)
    {

        // Display contact's first name.
        Console.WriteLine("First Name {0}: ", rec[0]);
        List<SalesOrderHeader> list = rec[1] as List<SalesOrderHeader>;
        // Display SalesOrderHeader information 
        // associated with the contact.
        foreach (SalesOrderHeader soh in list)
        {
            Console.WriteLine("   Order ID: {0}, Order date: {1}, Total Due: {2}",
                soh.SalesOrderID, soh.OrderDate, soh.TotalDue);
        }
    }
}

A continuación se muestra el ejemplo del método del generador de consultas.

Dim lastName = "Zhou"

Using context As New AdventureWorksEntities()
    ' Define a query that returns a nested 
    ' DbDataRecord for the projection. 
    Dim query As ObjectQuery(Of DbDataRecord) = context.Contacts.Select("it.FirstName, it.LastName, it.SalesOrderHeaders") _
                                                .Where("it.LastName = @ln", New ObjectParameter("ln", lastName))

    For Each rec As DbDataRecord In query.Execute(MergeOption.AppendOnly)

        ' Display contact's first name. 
        Console.WriteLine("First Name {0}: ", rec(0))
        Dim list As List(Of SalesOrderHeader) = TryCast(rec(2), List(Of SalesOrderHeader))
        ' Display SalesOrderHeader information 
        ' associated with the contact. 
        For Each soh As SalesOrderHeader In list
            Console.WriteLine(" Order ID: {0}, Order date: {1}, Total Due: {2}", _
                              soh.SalesOrderID, soh.OrderDate, soh.TotalDue)
        Next
    Next
End Using

string lastName = "Zhou";
using (AdventureWorksEntities context =
    new AdventureWorksEntities())
{
    // Define a query that returns a nested 
    // DbDataRecord for the projection.
    ObjectQuery<DbDataRecord> query =
        context.Contacts.Select("it.FirstName, "
            + "it.LastName, it.SalesOrderHeaders")
        .Where("it.LastName = @ln", new ObjectParameter("ln", lastName));

    foreach (DbDataRecord rec in
        query.Execute(MergeOption.AppendOnly))
    {

        // Display contact's first name.
        Console.WriteLine("First Name {0}: ", rec[0]);
        List<SalesOrderHeader> list = rec[2]
            as List<SalesOrderHeader>;
        // Display SalesOrderHeader information 
        // associated with the contact.
        foreach (SalesOrderHeader soh in list)
        {
            Console.WriteLine("   Order ID: {0}, " +
                "Order date: {1}, Total Due: {2}",
                soh.SalesOrderID, soh.OrderDate, soh.TotalDue);
        }
    }
}

Vea también

Tareas

Cómo: Usar rutas de la consulta para dar forma a los resultados (Entity Framework)

Conceptos

Consultar un modelo conceptual (Entity Framework)
Definir y administrar relaciones (Entity Framework)